1. Related Field
This invention relates to manufacturing vehicle bodies.
2. Related Art
A crucial part of automobile design is making the body of the vehicle sufficiently strong to protect the occupants in the event of a crash, and sufficiently stiff to prevent bending or torsion of the body from affecting the vehicle's handling. One way of making a relatively strong body is to use a composite tub, for example as described in EP 2 534 029 A.
A typical composite tub has a floor, sills upstanding from the floor along the sides of the floor and front and rear bulkheads upstanding from the floor at the front and rear of the floor. The vehicle's running gear and powertrain can be attached to the front and rear bulkheads. For an open racing car this structure may be sufficient, but for a passenger car or an enclosed racing car it is normally desirable to fit a roof to the tub. This is normally done by forming the roof separately and then attaching it to the tub: either by bolting it in place or by bonding it to the tub using adhesive. Using bolts is undesirable because it introduces additional weight and concentrates the loads between the roof and the tub on the areas to which the bolts are attached. FIG. 1 shows an adhesive join between a tub and a roof. FIG. 1 is a cross-section through the join, showing part of a tub 1, part of a roof 2, and a layer 3 of adhesive between the tub and the roof. Joints of this type suffer from a number of limitations. First, because the structures involved are of a considerable size, and because the integrity of the bond between the roof and the tub is of great importance for crash-worthiness, the adhesive joins are typically large. As a result, the adhesive introduces considerable additional mass. Second, it is difficult to ensure a perfect fit between the roof and the tub. One or both of the components may need to be machined in order to get them to fit together. Any machining introduces additional time and cost. Third, there is normally an abrupt end to the overlap between the roof and the tub, as shown at 4, and a significant spacing between the roof and the tub because of the thickness of the adhesive. This concentrates stress on the tub, reducing its strength. Finally, because the roof and the tub are rigid when they are married together, the tub cannot have undercuts in the area where it will be bonded to the roof. As illustrated in FIG. 2, if the bottom of the roof 2 is sufficiently wide that it can be lowered on to the tub 1, it cannot make contact with the tub at the undercut region 5. This limits design freedom unless it is decided to do without the roof material bridging the join between the roof and the tub; in which case strength would be compromised.
It would be desirable to have an improved way of attaching a roof to a tub.